OPTICAL STUDY OF THE ELECTRONIC STATES OF IN0.53GA0.47AS/IN0.52AL0.48AS QUANTUM-WELLS IN HIGH ELECTRIC-FIELDS

Absorption and electroabsorption spectra of (In,Ga)As/(In,Al)As quantum wells and superlattices, grown lattice matched to InP substrates, have been studied and compared with model calculations. Heavy-hole excitons dominate the spectra of uncoupled wells. They respond very sensitively to electric fields, mainly by losing oscillator strength to forbidden transitions. The ground state shows the pronounced red shift predicted from the quantum-confined Stark effect. A substantial increase of the electron mass with energy is observed. This nonparabolicity of the conduction band can be approximated by a linearly increasing mass, i.e., m(e)/m(0) = 0.041 + 0.045E/(1 eV). Superlattices with thin barriers develop minibands whose spectra are very different from those of uncoupled wells. Features arising from M0 and M1 singularities of the joint density of states allow direct measurement of the width of the minibands and yield a conduction-band discontinuity of 505 +/- 5 MeV. With increasing electric fields, the miniband structure is altered gradually. The oscillator strength in interband transitions is moved to the center of the band at transition energies corresponding to heavy- and light-hole excitons in uncoupled wells.